Magnetic fields in the 3C 129 cluster

We present multifrequency VLA observations of the two radio galaxies 3C 129 and 3C 129.1 embedded in a luminous X-ray cluster. These radio observations reveal a substantial difference in the Faraday Rotation Measures (RMs) toward 3C 129.1 at the cluster centre and 3C 129 at the cluster periphery. After deriving the density profile from available X-ray data, we find that the RM structure of both radio galaxies can be fitted by a tangled cluster magnetic field with strength 6 muG extending at least 3 core radii (450 kpc) from the cluster centre. The magnetic field makes up a small contribution to the total pressure (5 per cent) in the central regions of the cluster. The radio morphology of 3C 129.1 appears disturbed on the southern side, perhaps by the higher pressure environment. In contrast with earlier claims for the presence of a moderately strong cooling flow in the 3C 129 cluster, our analysis of the X-ray data places a limit on the mass deposition rate from any such flow of < 1.2 M-. yr(-1).